The present invention relates to a photosensitive resin composition for printing screens. More specifically, it is concerned with a new photosensitive resin composition in solution including, as a sensitizer, a photosensitive vinyl monomer or prepolymer which has not been used hitherto as a material for the so-called direct process for producing printing screens, a presensitized printing screen produced therefrom, and a process for producing the same.
Photosensitive film materials for printing screens which have been heretofore used comprises an aqueous emulsion mixture of polyvinyl alcohol and polyvinyl acetate to which ammonium bichromate or diazo resins are added as a sensitizer. These photosensitive materials are very suitable for use in producing printing screens. However, they are unsatisfactory with respect to preservability. Further, the photosensitive materials containing bichromates as a sensitizer are limited in their use because of chromium pollution problems. At the present stage, diazo resins are being principally used as a sensitizer.
Diazo resins have excellent non-pollution property and preservability as compared with the bichromates, and when they are coated on a screen and dried to form a photosensitive film thereon, the film can be stored in cold and dark places for about one week. However, under the preservation conditions of normal temperature and humidity, a so-called dark reaction occurs, which makes even the non-exposed areas of the film insoluble in water. As a result, such a film becomes useless. Therefore, when the above mentioned photosensitive materials are used, coating, exposure and washout development operations must be carried out as rapidly as possible and in a continuous manner. Accordingly, there exist a great number of inconveniences in producing printing screens.
For example, when screen process printing is effected in a remote place in the production of electronic components, a printing screen is usually produced in situ, whereas coating of the photosensitive material onto screens may still be advantageously and conveniently carried out by a supplier of the photosensitive material for the printing screens. In this case, screens with a photosensitive film coated thereon (presensitized printing screen) must be delivered to an electronic component plant in a remote place. Accordingly, there is a demand for a photosensitive film for printing screens which can be safely stored under normal temperatures and humidities for a long period of time.